1. Field of the Invention
The subject invention pertains to the field of transmission lines and more particularly to a surface wave guiding structure which is self-supporting and exhibits minimum attenuation and dispersion characteristics.
2. Description of the Prior Art
Communication and short electromagnetic guided wave reflectometer control systems for constrained vehicle ground transportation require guiding structures along the right of way. These guiding structures must exhibit minimum attenuation and dispersion characteristics, must possess surface wave fields that extend a sufficient distance from the structure to couple to the vehicle and objects placed adjacent to the right of way, must be self-supporting, and must operate reliably in adverse weather conditions. Surface wave and leaky wave transmission lines such as the dielectric image line, Goubau line, slotted and braided coaxial lines, and trough and W-lines do not possess all these required characteristics. Dielectric image lines are highly dispersive and cause significant pulse broadening which degrades the range resolution of the system, while conventional Goubau lines are not self-supporting and are adversely affected by environmental conditions such as ice and snow. Leaky coaxial cables exhibit excessive loss and quasi TEM lines such as the W-line and a metallic and dielectric shielded Goubau lines, due to the shielding thereof are very insensitive to external objects. A transmission line disclosed in U.S. Pat. No 4,188,595, issued Feb. 26, 1980 by Cronson et al and assigned to the assignee of the present invention is self-supporting, exhibits the required electrical properties, and provides significant improvement in environmental protection over the other transmission lines in the prior art. Applications exist, however, that require environmental protection which exceeds even that provided by the transmission lines disclosed by Cronson et al.
The present invention provides a self-supporting surface wave guiding structure for vehicle control and communication systems, which exhibits minimum attenuation and dispersion characteristics and provides environmental protection that exceeds the protection provided by the transmission line disclosed in U.S. Pat. No. 4,188,595.